One of the most common arrangements for moving large quantities of heavy material such as overburden from strip mining operations, earth from excavation operations, and other similar material movement, is to load/utilize large trucks. Loading of the trucks is accomplished by means of front end loaders, electric/hydraulic shovels, or conveyor systems.
In terms of front end loaders and electric/hydraulic shovels, large buckets are filled with material and then swung into position over the truck where the material is dumped. Cycle times for loading a truck are dependent on the size of the buckets and the speed of the loaders/shovels. The current state-of-the-art uses 13-22 yard capacity loader/shovels while the trucks have at least five times this capacity. Cycle time for the scooping and dropping of a load is on the order of 40 seconds or more. Thus, loading cycle times are on the order of 3-4 minutes.
In terms of conveyor systems, material is pushed onto one end of a conveyor and conveyed to the other end of the conveyor which hangs over the truck bed. However, standard heavy-duty conveyor systems are nominally 6-8 feet wide while the equipment (e.g., bulldozers) used to push material to the conveyor can be up to 22-24 feet in width. Accordingly, a variety of conveyor feed systems have been developed to funnel the delivery area into the narrower conveyor width. Such feed systems include those disclosed in U.S. Pat. Nos. 4,011,936.
In U.S. Pat. No. 4,011,936, a conveyor apron is initially at ground level and is filled with material. The apron is then pivoted upward to allow the material to be gravity fed onto the conveyor. However, this results in down time in terms of loading the apron since the apron must be lifted off the ground to get the material onto the moving conveyor. This increases the overall loading cycle time. Further, this system is not well suited for large size material encountered in strip mining overburden.